Which of your pets are you most looking forward to upgrading to rare? Since I don't expect the battle stones to be very common or cheap, I'm making a list of my priorities for each family, and I'm curious what other people are planning. Do you want to upgrade that poor Minfernal or Scourged Whelpling? Or would you rather upgrade one of the pre-MoP pets with an interesting moveset that you've been neglecting due to its Uncommonness?

Undead: this is my top priority overall -- Ghostly Skull. He has two nasty burst damage abilities and can self-heal with Death Coil, or he can choose Unholy Ascension, which is unique to him and provides a ton of extra damage for your later pets. My only hesitation is that he has 3 breedIDs, and I'm not sure which I like best. I also have a rare Scourged Whelpling already, which made this choice a bit easier.

Magic: no, not Minfernal! -- even though mine is poor. I'm leaning toward Enchanted Broom, since he's incredible against Aquatics and has a neat unique ability in Sweep.

Mechanical: so many choices, due to all the old Engineering pets: I'll probably choose Mechanical Pandaren Dragonling, since he's great against Magic pets and is similar to Darkmoon Zeppelin, which I like a lot.

Humanoid: probably Winter's Little Helper, due to a potentially vicious moveset of Call Blizzard, Ice Lance, and Gift of Winter's Veil. I'd much rather not use battle stones on wild pets, but I might break down and upgrade a Flayer Youngling with the right breedID, since there's 10 breeds and finding a rare of the one I want is a bit daunting.

Yes, just as you guessed: many pets can come with different combinations of stats. Warla compiled a nice list of the possibilities at http://schaffhauser.me/Warcraft#PetBreeds. So for example Scourged Whelpling comes in two varieties: he can have 1806 health at level 25 as a rare, or 1481 health, with a tradeoff of gaining some speed and power.

The Flayer is an extreme case, because he's got 10 different stat combinations (breedIDs). I'd like the fastest one since his Kick ability benefits from going first, but trying to get that perfect 1 rare out of 10 is pretty tough, considering this guy is pretty heavily farmed to begin with.

Has it been confirmed that a pet will maintain its breed ID after using an upgrade stone on it? For example, I finally caught a rare quality Tiny Twister the other night, but saw (using that awesome tool) that my poor quality Tiny Twister has a better breed ID.

I'm sorry I was under the impression the upgrade stones would only work on wild pets, since they're the only one with various quality levels.. but it sounds like we will be able to use them on pets from other sources too?What if you use one on a pet that is normally always Rare, will it get epic? :O

Anywho, my first stone will probably be going on my Uncommon Fel Flame because I'm tired of farming for a rare one

Crawling Claw and Lil' Tarecgosa are already rare and won't need a stone -- I believe that 5.1 will also color in the borders of pre-MoP pets so it'll be easier to know their rarity at a glance and we can avoid re-raring our rares. And, hopefully the stones will give an error message if you try to apply it to an already-rare pet.

The 5.1 stones strictly bump a pet to rare, regardless of its original rarity. So no epic for you, at least not in 5.1, although there are epic battle stones in the PTR game files that are likely to appear in game 'eventually' (per Blizz via Twitter). There will also be Justice Point-purchaseable stones that bump them to uncommon, but I think we're mostly ignoring those.

I don't actually know if pets will retain their breedID when you stone them. The most logical way to code it seems to be to simply increment the rarity all the way up to rare, and all this would do is apply a statmod(1.3) (versus 1.0 for poor, 1.1 for common, etc.), and change the border color. If it's coded this way then breedID would not be touched. But, when has Blizzard ever done it the simplest way? I haven't seen any info from PTR about how the stones work, so I can't say for sure. Personally, I'm operating on the assumption that breedID will stay the same.

I am also 99% sure that the battle stones will be usable on all battle pets, not just wild pets. Here's the PTR linky, it doesn't give a restriction, and pre-MoP pets all have a 'rarity' in the game code if not in their border color, so I think all pets are valid targets.

My first critter stone with certainly be going to my red cricket, of which my best friend Sho gave me only a poor quality(some best friend). As for the rest of my collection, I'm just not sure, but I do know that I wont be using the stones on wild pets.

Scourged Whelpling, Flayer Youngling #5, Rabbit #5, Mechanical Yeti, Perky Pug, Peanut, Ghostly Skull are all on the short list for upgrades. That's assuming of course that I don't find rares of the Whelpling, Rabbit, and Flayer before 5.1. Hopefully I do so I don't have to use stones on them although if I have to I will.